Hydro-Mechanical Properties of Some Potential Clay Liner Materials in Southwestern Nigeria

The influence of external applied stress on permeability of hydraulic barrier soils has not received adequate attention from researchers in recent times. The method of determining the coefficient of permeability (k) from back calculation from consolidation test is presented in this study. Special effort was made to derive a relationship between the coefficient of permeability and applied stress. Clay soil samples with potential for use as clay liners were taken in Akure, Southwestern Nigeria. Preliminary laboratory tests carried out on the samples include natural moisture content, particle size distribution test, pocket penetrometer test, and unconfined compression test. Consolidation test were performed on the soils, carefully simulating natural in-situ compression and the coefficient of permeability obtained ranged between 1.89 x 10-9 m/s and 1.35 x 10-11 m/s. Experimental results reported in this project indicate that permeability is inversely proportional to applied stress. For sample 1 when the pressure was 100 KN/m2, the coefficient of permeability was1.89 x 10-9 m/sec. however, when pressure rose to 3200 KN/m2, the coefficient of permeability dropped to 5.12 x 10-10 m/sec. Variation of voids ratio with progressive increment of applied pressure was monitored during the experimental programme. Statistical linear regression equation for the relationship between coefficient of permeability and the applied pressure gave a high coefficient of determination (0.985) with cubic polynomial best fit, which is close to 1, hence the best model for describing the relationship. Using the Samarasinghe, Huang and Drnevich, empirical relation between voids ratio and coefficient of permeability to validate the experimental results, log {k (1 + e)} - log e relationships have been obtained for the Akure clay soils. A comparison was made between the result obtained from the laboratory, the empirical Samarasinghe equation, and those reported by other authors. There was reasonable agreement to suggest that the coefficient of permeability values obtained from consolidation tests are reliable.